How to smooth edges of polygons?

I created a image (uint8) with multiple filled polygons. First, I used the vision.ShapeInserter with 'Antialiasing' but this was not enough. Also insertShape + 'SmoothEdges' produced insufficient smooth edges. Are there any other ways how I can fix that?

Looking forward to your suggestions. Thanks!

Answer 1

[Andrew Chen]

Perhaps imopen with a disk structuring element will provide the functionality you are looking for?

Ex:

se = strel('disk',5);
new_img = imopen(original_image,se);

Hope this helps!

[m975]

Hi Andrew and thanks for your answer! As you can see it did not really help. I guess the edges are too fine. Are there any other suggestions?

[Andrew Chen]

Did Image Analyst's answer get you what you wanted? Otherwise, maybe you could clarify what you mean by "smooth edges". What in your mind constitutes a sufficiently smooth edge?

[m975]

For example, in this image polygons show proper edges without these awful "stairs" when the shapes get rotated. By the way, this image was drawn in photoshop. But now I have to create a lot of stimuli in MATLAB by using coordinates for my polygons. Consequently, I am looking for a MATLAB routine to generate images of same quality. I hope this explanation helps. Thanks!

Answer 2

[Image Analyst]

You can smooth the edges with a filter. See attached.

[m975]

Thanks for the code! But is there is also an easier and more fundamental solution? Due to the fact that I create these polygons in MATLAB directly I cannot understand why the output of such simple shapes can be so bad. Could maybe a vector based format be the right way? Unfortunately, I did not find such a format for imwrite.

[Image Analyst]

I don't know how they were created and what they are. If they are images, are they grey scale, or binary? If they're binary images, you can smooth them nicely by blurring with conv2() or imfilter() and then thresholding.

[Image Analyst]

m975's "Answer" moved here because it's not an "Answer" to the original question, but a reply to me.

I opened an image with

image = zeros(PicHeight,PicWidth,3,'uint8') + 255;

and inserted polygons with the vision.ShapeInserter. Finally, I saved the images with imwrite as PNG.

[Image Analyst]

OK, then blurring should work, like I said. Did you try it? If not, why not?

blurredImage = imfilter(grayImage, ones(9)/81);

[m975]

Because I thought you need more information about the image. Now I tried it but it looks too blurish.

[Image Analyst]

It looks binary, so just threshold it. The corners should then be more rounded off.

[m975]

I processed the image as follows but it did not work.

level = graythresh(I);
BW = im2bw(I, level);

You can still see these toothed edges:

[m975]

Finally, the easiest workaround was to create very big images (5000 x 5000 px) and, subsequently, resize them to the favored stimulus size. Now edges look sexy again!